Return type of function properties in typescript declaration-CodePudding

I'm trying to fix the Typescript declaration for youtube-dl-exec, which has a default export which is a function with properties. In short, the default export returns a promise, alternatively you can call the exec() method which returns a child process so you can monitor the progress without waiting for the promise to resolve.

The existing declaration works for the default function, but not any of the properties:

import ytdl from 'youtube-dl-exec';
const p = ytdl('https://example.com'); // p is Promise<YtResponse>
const r = ytdl.exec('https://example.com'); // r should be ExecaChildProcess
// ^ property exec does not exist … ts(2339)

What I've come up with so far is this declaration:

declare module 'youtube-dl-exec' {
  type ExecaChildProcess = import('execa').ExecaChildProcess;

  const youtubeDl = (url: string, flags?: YtFlags, options?: Options<string>) => Promise<YtResponse>;
  youtubeDl.exec = (url: string, flags?: YtFlags, options?: Options<string>) => ExecaChildProcess;

  export default youtubeDl;
}

Now the existence and signature of exec is seen by Typescript, but with the return type of any. I don't think the type import is a problem, indeed even if I change the return type to a primitive string the Typescript compiler still sees the return type of exec as `any.

Since the assignment of the function property almost works, I feel like I'm on the right track, but can't figure out how to specify the return type of this function property.

CodePudding user response：

This in implemented by either using namespace

  type ExecaChildProcess = import('execa').ExecaChildProcess;

  declare const youtubeDl: (url: string, flags?: YtFlags, options?: Options<string>) => Promise<YtResponse>;
  declare namespace youtubeDl {
    export const exec: (url: string, flags?: YtFlags, options?: Options<string>) => ExecaChildProcess;
  }
  export default youtubeDl;
}

or merging function type with object type

declare module 'youtube-dl-exec' {
  type ExecaChildProcess = import('execa').ExecaChildProcess;

  declare const youtubeDl: (
    (url: string, flags?: YtFlags, options?: Options<string>) => Promise<YtResponse>
  ) & {
    exec: (url: string, flags?: YtFlags, options?: Options<string>) => ExecaChildProcess;
  }

  export default youtubeDl;
}